The present invention concerns improvement in a process for preparing D-alloisoleucine, which is useful for preparing medicines, particularly, drugs for cardiovascular disease (typically, WO94/28,901), and a novel complex which occurs as the intermediate in the process of preparation thereof. The invention also concerns an improved process for epimerizing L-isoleucine for the purpose of producing D-alloisoleucine from L-isoleucine.
The present invention makes it possible to produce D-alloisoleucine, which has not been available in a large quantity, from L-isoleucine which is commercially mass-produced, by a simple process at a high yield.
In this specification RS-indication is used in relation to the configuration of tartaric acid and derivatives thereof. This is because the conventional DL(or dl)-indication may cause confusion, in fact, in the past there was a case where one researcher regarded an isomer as D-form while another indicated the same compound as L-form. As far as amino acids are concerned there is no such problem and thus conventional DL-indication is used. The term "isomerization" is used to encompass both racemization and epimerization. In some cases these are represented by the term "racemization".